For the purpose of pathological diagnosis, a living cell may be microscopically observed. In many cases, a living cell has to be sliced to a thickness of several micrometers to 10 micrometers.
When a living cell is observed without being sliced, an observation operation becomes more efficient in terms of time. Accordingly, observation techniques without slicing a living cell are expected.
A confocal microscope may be used for observation of a sample such as a living cell (c.f. Patent Document 1). The confocal microscope is excellent in resolution in an optical axis direction.
The confocal microscope includes an objective lens, a detection lens, a pinhole member and a detector. The objective lens condenses a beam toward a sample. The sample reflects the beam condensed by the objective lens. The detection lens condenses a reflected beam from the sample. The pinhole member is arranged so that a pinhole formed in the pinhole member coincides with a position at which the detection lens makes the beam condensed. The detector detects the reflected beam passing through the pinhole. Accordingly, there is a high resolution in the depth direction of the sample. Consequently, it is not necessary to thinly slice the sample.
In general, a living cell has high transparency and low reflectance. In addition, there is a very small change in refractive index of a living cell. Accordingly, the detector may detect very small power or light quantity of the reflected beam. Consequently, the resultant image is likely to be dark.
It may be considered that an increase in power of a light source emitting a beam toward the sample results in an increase in a light quantity of the reflected beam. The increase in power of the light source, however, may result in optical or thermal damage to a sample such as a living cell. Therefore, the increase in power of the light source may not be a suitable method for acquiring a bright image.
The aforementioned problems are common not only to observation of a living cell but also to observation of another sample which causes little reflected light.
Patent Document 1: JP S61-140914 A